SAN BRUNO, Calif. (AP) — Police and federal agents converged Tuesday on YouTube's headquarters in the San Francisco Bay Area after receiving numerous reports of a shooting. A hospital said it received four or five patients without providing further details.

Police in the city of San Bruno said there was an active shooter but did not immediately provide more information. Multiple 911 calls reported gunfire, and police and fire officials swarmed the area, City Manager Connie Jackson said.

Television news footage showed people leaving the building in a line, holding their arms in the air for police to inspect as they were leaving the building.

Officers patted down people to make sure none had weapons, and police vehicles surrounded the area. Northern California's Stanford Hospital said it has received four to five patients, but a hospital spokeswoman did not have information on their conditions or their wounds.

Google, which owns the world's biggest online video website, posted on Twitter that the company is coordinating with authorities. The Bureau of Alcohol, Tobacco, Firearms and Explosives also said it responded to the shooting at YouTube's suburban campus.

The White House said President Donald Trump was briefed on a shooting at YouTube headquarters and that officials were monitoring it.

Coroner's spokesman Thomas McGovern says investigators were called to the scene Tuesday afternoon. He would not say if anyone was dead.

YouTube employee Vadim Lavrusik posted on Twitter that he heard gunshots and saw people running. He said he was barricaded in a room with his co-workers before being safely evacuated.

Will Hudson said a friend who works for YouTube texted him about the shooter.

"I think there might be a shooter in my building," read one text. "The fire alarm went off so we started to evacuate and then people (started) running saying there was a shooter."

Hudson said the friend made it safely back to San Francisco and was in contact with his family. Hudson said he's become used to hearing about gun violence but has never been so close to it before.

"It just feels strange. It feels like it could really be anyone. That's really the strangeness of it," he said.

Calls and emails to YouTube representatives seeking comment were not immediately returned.